PROJECT SUMMARY/ABSTRACT The developmental transition from adolescence to young adulthood is characterized by escalations in both substance use and body dissatisfaction (BD; negative, subjective evaluation of one's shape and weight). BD predicts onset of multiple adverse developmental outcomes. By young adulthood BD affects the majority of women and men, although prevalence and intensity of concern with overweight is higher among women. Substance use and BD are typically studied independently, but elevated rates of problematic drinking and cigarette use among youth with BD suggest the need for research on pathways to substance use and differential approaches to preventing substance use for young adults with BD. This study aims to capture the temporal sequencing of BD and alcohol and nicotine use on a daily time scale, test potential mechanisms linking BD to alcohol and nicotine use, and examine person and day characteristics that moderate these associations. This study addresses two NIDA research priorities: gender-related differences in pathways to substance use and mechanisms of comorbidity between substance use and other health concerns. This study will yield rich data on nicotine vaping/electronic nicotine delivery system use, which has recently emerged as a significant public health concern among youth. Aim 1 is to investigate links between trait BD and weekly alcohol and nicotine use and person-level characteristics that moderate these links. Aim 2 is to investigate within-person prospective links between daily BD and same- and next-day alcohol and nicotine use and day- level characteristics that moderate these links. Aim 3 is to examine daily negative affect and weight control motivations as mediators of within-person links between daily BD and same- and next-day alcohol and nicotine use, respectively. To achieve these aims, the applicant will conduct a 14-day daily diary study of 125 college students, yielding up to 1,750 daily observations and 125 baseline surveys. The analytic approach will include regression analyses (Aim 1), multilevel modeling (Aim 2) and multilevel structural equation modeling (Aim 3). This study will advance scientific knowledge on the co-occurrence of BD and alcohol and nicotine use among young adults and inform development of real-time interventions for a vulnerable population. The applicant's exceptional mentor team has expertise in statistical analysis and intensive longitudinal methods (Stephanie Lanza), young adult development, gender, and gendered health disparities (Susan McHale), substance use and implementation of daily diary studies (Gregory Fosco), and BD (Alison Field) and will guide the applicant's development into an independent researcher. The applicant seeks training in the etiology of alcohol and nicotine use, BD and gender, intensive longitudinal methods, professional development and research dissemination, and the responsible conduct of research. This training and research will position the applicant to make substantial contributions to our understanding of the comorbidity between BD and substance use as well as gender differences in pathways to substance misuse throughout her career.